Desulfurization of fluid petroleum coke

ABSTRACT

A METHOD FOR REMOVING METALS AND SULFUR FROM PETROLEUM COKE BY PARTIAL GASSIFICATION OF THE COKE WITH STEAM AT ELEVATED PRESSURES AND TEMPERATURS. GASIFICATION OF LESS THAN APPROXIMATELY FIFTY PERCENT OF THE COKE WITH STEAM AT PRESSURES RANGING FROM ABOUT 100 TO 3,000 P.S.I.G. RESULTS IN SELECTIVE DISULFURIZATION OF THE UNCONVERTEDD COKE. TEMPERATURES RANGE FROM ABOUT 800 UP TO ABOUT 2500*F. THE EXTENT OF GASIFICATION RANGES FROM ABOUT 5 TO 50% OF THE COKE.

United States Patent 3,600,130 DESULFURIZATION 8F FLUID PETROLEUM C Clyde L. Aldridge and Robert H. Waghorne, Baton Rouge, La., assignors to Esso Research and Engineering Company No Drawing. Filed Mar. 24, 1969, Ser. No. 809,937 Int. Cl. C01b 31/02 US. Cl. 23-2093 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention This invention relates to improvements in desulfurizing coke particles containing high percentages of sulfur. More particularly, it relates to the desulfurization of high sulfur petroleum coke particles from fluid or delayed coking processes by subjecting the coke particles to a gasification treatment with steam at elevated temperatures and pressures.

Description of the prior art Prior art processes for desulfurization of petroleum coke have involved the combined treatment of coke comprising steam treatment at high temperatures with the addition of hydrogen at pressures ranging from about 1 atmosphere to about 5 atmospheres. Typical of these is US. Pat. 3,007,849 wherein the patentees utilize a process having a steam treatment followed by hydrogen treatment at 1200 to 1700 F. whereby the sulfur content of the fluid coke is reduced to about 4 wt. percent. One of the major disadvantages of using this process is the utilization of relatively expensive hydrogen in desulfurizing the fluid coke. Additionally, multiple treatments add to costs involved.

Coking has its greatest utility in upgrading the quality of low grade petroleum vacuum residua and pitches from highly asphaltic and sour crudes. Such residua frequently contain high concentrations of sulfur, i.e. 3 wt. percent or more. In general, the sulfur content of the coke product from the fluid or delayed coking processes is about 2 times the sulfur content of the residuum feed from which it is produced. The sulfur content of coke from sour residu'a thus can range from as much as 5% to 8% sulfur or more.

The high sulfur content of the coke product poses a mag'or problem in its efficient utilization. For many nonfuel or premium fuel uses a low sulfur content coke, about or below 4 wt. percent sulfur is required. For utilization of coke in the manufacture of certain metals the sulfur content should be substantially lower than the 4%.

The conventional methods of removing sulfur from co'ke from ordinary sources with gaseous reagents have in general not been too satisfactory. The results are even poorer when these procedures are applied to fluid coke as compared to delayed coke or coal. This is due to the fact that treating gases have relatively no access to the 3,60,130 Patented Aug. 17, 1971 'ice sulfur contained in the coke particles. Fluid coke is laminar in structure and may comprise some 30 to superposed layers of coke. Thus, it is difiicult for a reagent to penerate more than a few outer layers. These difficulties in desulfurizing fluid coke are further aggravated by the higher than normal sulfur content of this coke derived from high sulfur petroleum feeds.

This invention overcomes the above difiiculties and disadvantages by providing an improved process for desulfurizing high sulfur containing petroleum coke with steam at elevated temperatures and pressures. In particular, the process comprises partially gasifying petroleum coke with steam under elevated temperatures and pressures, if desired in the presence of a suitable catalyst, for example, K CO whereby the sulfur content of the petroleum coke is reduced to below about 1.5 wt. percent.

SUMMARY OF THE INVENTION The present invention provides an improved process of lowering the sulfur content of petroleum coke comprising partially gasifying the coke with steam, at a temperature ranging from about 800 to about 2500 F. and at pressures ranging from about 100' to about 3000 pounds per square inch gauge (p.s.i.g.), the coke being gasified to the extent of from about 5 to about 50 weight percent. Preferably, the reduction of sulfur in the unconverted coke is to less than 1.5 weight percent remaining therein, and ideally, to less than 1.0 percent by weight remaining in the unconverted coke.

The reaction may be conducted in the presence of an alkali metal carbonate catalyst, or other suitable steamcoke catalyst. The partial gasification of the petroleum coke is best accomplished using gas (steam) velocities of greater than 0.1 foot per second in either fixed or fluid bed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS It has been found that in gasifying the petroleum coke in the presence of a gasification catalyst, the alkali metal carbonates, such as, potassium carbonate (K CO and sodium carbonate (Na CO were of most benefit to the invention. Of particular usefulness is the K CO in an amount ranging up to 50 percent by weight based on the coke. However, these quantities of K CO are economically impractical. Therefore, it was discovered that excellent gasification, balanced against costs, could be achieved using K CO in amounts ranging between about 1 and 25 weight percent. Most suitably, the amounts of K CO useful in the invention ranged from about 2 to about 10 weight percent, based on the coke.

It has been discovered that other variable factors can be altered to affect the gasification rate. One of the most important is the gas (steam) velocity, which should be greater than about 0.1 foot per second (ft./sec.). Preferably, gas velocities may vary from 0.05 ft./sec. up to about 2.0 ft./sec., the most preferred range, however, being from 0.1 to 0.4 ft./sec.

Concurrently, it is important to have water feed rates that are compatible with the above gas velocities. Generally, the steam feed rate ranges from 0.1 to about 20 w./w./hr. At these rates, and under suitable conditions of temperature and pressure, as hereinafter specified, it is possible to obtain steam conversion of greater than twenty-five (25) percent. Most suitably, the steam feed rate should range from 1 to about 8 w./w./hr., depending on the temperature and pressure under which gasification is occurring.

Good gasification and sulfur removal from the remaining coke has been achieved employing temperatures between about 800 and 2500 F. When catalysts are used, the temperature preferably ranges from about 800 to about 1600 F., while temperatures of between about 1600 to about 2000 F. are most preferable in the absence of a catalyst. Temperatures ranging from about 1000 up to about 1500 F. are most preferred in the presence of a catalyst.

It has been discovered that at the above temperatures, petroleum coke can be gasified at up to about 110 percent per hour, especially at pressures ranging from about 200 p.s.i.g. up to about 1000 p.s.i.g. The higher pressures within the preferred range are desirable due to the fact that such pressures would reduce the requirement of subsequent compression of the hydrogen produced by the reactions involved. Thus, pressures ranging from 200 to about 850 p.s.i.g. would be most suitable in the invention, the upper ranges being the most preferred.

The coke particle size is dependent upon the conditions under which the petroleum coking occurs. The present process may be applied generally to fluid or delayed cokes in their commercially available form. If desired, the particle size may be reduced for particular equipment requirements.

One of the important factors in the present desulfurization process is the absence of added hydrogen. The addition of hydrogen tends to reduce the rate of gasification of the coke. Best reaction rates are obtainable by adding steam only within the gas velocities and under the temperature and pressure indicated above. Thus, it has been found that gasification of fluid coke of about to 30 percent removed 77 to 86 percent of the sulfur in the fluid coke. This is more particularly shown in the example, below.

Example 1 Using a fixed bed reactor charged with 33 grams of Billings Green fluid coke, steam was added thereto at 1400 F. The amount of steam added to the reactor was about 1 weight of water per weight of coke per hour (w./w./ hr.).

Treatment of the fluid coke with steam, in this run, was accomplished in three successive periods, with initial pressure of 300 p.s.i.g., then atmospheric, and subsequently at 300 p.s.i.g. The exit gas was cooled to condense unconverted water and a sample of the dry gas collected at the end of each period and analyzed. Hydrogen sulfide contents are tabulated below. In each case the dry gas contained the expected mixture of hydrogen, carbon monoxide, car-bon dioxide and methane.

Examination of the data, above, reveals that the quantity of H 8 removed from the coke and evolved into the product gas is much less at atmospheric pressure than at 300 p.s.i.g.

Examples 2-4 A fixed bed reactor was prepared in the same manner as in Example 1, above, again with Billings fluid coke. The fluid coke was partially gasified with steam at 1400 F. and 280 p.s.i.g., both with and without a gasification catalyst (Nos. 2 and 3 without catalyst). The Billings fluid coke sample used in these runs contained 5.85 Weight percent sulfur. The results of the three desulfurization runs are given hereinbelow.

1 Catalyst was :KgCOg.

4 Results indicate that under these conditions, sulfur is being selectively gasified about 3 to 4 times as fast as the carbon, and that -90 percent of the sulfur is being removed together with 18-27 percent of the carbon.

Example 5 Partial gasification of a sample of a Billings fluid coke sample, similar to the sample used in Example 1, at a pressure of 850 p.s.i.g. and at a temperature of 1200 F. resulted in reduction of sulfur content of the remaining fluid coke from 5.7 weight percent down to 0.2 weight percent. Treatment of the coke with steam, in the presence of K CO catalyst, resulted in a 33 percent gasification of the coke.

Example 6 A fixed bed reactor was prepared, as in Example 1, with a Billings fluid coke sample and with K CO as a catalyst. The coke was partially gasified with steam at 1400 F., but at atmospheric pressure. The contact period was greatly extended over that ordinarily employed when pressures greater than atmospheric are used. This was done in order to get up to about 66 percent gasification of the coke. The remaining coke had a residual sulfur content of 3.05 weight percent. This run illustrates the dramatic effect of conducting the gasification reaction under pressure, as shown in the other runs.

Example 7 In a fluid bed, 1100 pounds of fluid coke containing 5.3 weight percent sulfur, and to which had been added 10 weight percent K CO was treated for a period of eleven (11) hours at 1200 F. and 200 p.s.i.g. with steam at the rate of 0.2 W./w./hr. at a linear gas velocity of 0.3 feet per second. The coke was originally prepared from a high vanadium content Caribbean residuum. At the end of the above treatment it was determined that the coke had been 35 percent gasified, and the remaining coke had a residual sulfur content of 1.1 weight percent.

Example 8 Using a fixed bed type reactor, 1000 pounds of a delayed coke, prepared from a Caribbean residuum, and having a 5 percent sulfur content is treated in the same manner as the fluid coke sample in Example 3, i.e., in the absence of a catalyst at 1400 F. and 280 p.s.i.g. Gasification is over thirty (30) percent, while the remaining coke has a residual sulfur content of less than 1.5 weight percent.

The method of the invention contemplates the use of a suitable gasification catalyst, such as potassium carbonate. The catalyst is easily mixed with the petroleum coke prior to its being charged to the reactor. As a rule, the catalyst is recoverable by conventional methods. There may be a slight overall catalyst loss however.

The importance of using a catalyst can be seen in the fact that metals removal, particularly vanadium, is possible by simple water washing if the catalyst is used in the desulfurization step. Generally, such a process would comprise charging the coke-catalyst mixture to a pressure reactor, pressurizing to the level specified above, at a temperature of about 1000 up to 1500 F. and treating with steam. The product gas is taken off, water recovered and hydrogen purified. The desulfurized coke is removed and water Washed, which removes the vanadium and most other metals. If a fluid coke from Venezuelan crude were being desulfurized, there would be about 0.36 weight percent vanadium therein subject to removal by the present invention.

If no catalyst is used, the desulfurization requires a temperature of from about 1500 up to about 2500 F., preferably from 1600 up to 2000 F. One of the disadvantages of not using a catalyst is that metals removal is not possible by the water washing step.

Both catalyzed and non-catalyzed methods may be used in most conventional reactors suitable for desulfurization. Generally, the fluidized or moving bed type reactors would be suitable. Likewise, other suitable contacting means would be acceptable, including reactors adapted for staged operations.

It is felt that the present invention would be equally suitable in desulfurizing shale oil and tar sands products which are compatible with steam treatment processes.

Steam addition to the reactor is variable over a fairly broad range while achieving satisfactory desulfurization. Steam may be added in an amount ranging from about 0.05 up to about 20.0 w./w./hr. A more preferred range is from 0.1 up to about 10.0 w./w./hr., with best results being obtained with a steam addition ranging between 0.2 and 4 w./w./hr.

These steam additions, particularly the more preferred ranges, at the preferred temperatures and pressures, provide a coke gasification rate of up to about 100 percent per hour. Naturally, higher gasification rates enable achievement of gasification in a shorter period of time (thus reducing contact time for the coke being desulfurized). Therefore, depending on gasification rates chosen, solid contact times will range from about 5 minutes up to about 6 hours, or more. Preferably, solid contact time should be within 15 minues to about 2 hours.

Besides providing a relatively inexpensive source of hydrogen, the present process provides a desulfurized coke product extremely well suited for blast furnaces in iron making. When the vanadium is extracted from the desulfurized coke, the product is useful in high grade aluminum manufacture.

What is claimed is:

1. A process for the partial desulfurization of fluid coke which' comprises contacting the fluid coke with steam at a temperature between about 800 and 1600 F.,

at a pressure between about 200 and 1000 p.s.i.g., and in the presence of a gasification catalyst until from about 5 to about weight percent of the fluid coke has been gasified and until the sulfur content of the unconverted fluid coke has been reduced to less than about 1.5 weight percent, based on the remaining coke.

2. A process according to claim 1 wherein the temperature ranges from about 1000 to about 1500 F., the pressure ranges from about 200 to about 850 p.s.i.g., and the catalyst is potassium carbonate.

3. A process according to claim 2 wherein the potassium carbonate is present in the reaction in an amount ranging from about 2 and about 10 weight percent, based on reactor charge.

4. A process for the partial desulfurization of fluid coke which comprises contacting the fluid coke with steam at a temperature between about 1600 and about 2500 F and at a pressure between about 200 and about 1000 p.s.i.g. until from about 5 to about 50 weight percent of the fluid coke has been gasified and until the sulfur content of the unconverted fluid coke has been reduced to less than about 1.5 weight percent, based on the remaining coke.

References Cited UNITED STATES PATENTS 2,201,050 5/1940 Oberle 23-209.9X 2,682,455 6/1954 Gorin 48197 2,840,462 6/1958 Gorin 48-197 3,007,849 11/1961 Nelson et al. 20117 3,387,941 6/1968 Murphy et a1 23--209.9

EDWARD J. MEROS, Primary Examiner US. Cl. X.R. 201-17 

